Process for the preparation of 1,1,1-trifluoro-2,2-dichloroethane

ABSTRACT

The invention relates to a process for the preparation of 1,1,1-trifluoro-2,2-dichloroethane (F 123 ).  
     This process consists in bringing 1,1,1-trifluoro-2-chloroethane (F 133   a ) into contact with chlorine in the presence of hydrogen fluoride and of a fluorination catalyst.  
     The F 133   a  can be obtained by chlorination of trichloroethylene and the F 123  can subsequently be fluorinated to F 125.

[0001] A subject-matter of the present invention is a process for thepreparation of 1,1,1-trifluoro-2,2-dichloroethane (F123) by catalyticchlorination of 1,1,1-trifluoro-2-chloroethane (F133 a) in the presenceof hydrogen fluoride (HF). The invention also relates to the applicationof this process to a process for the manufacture of pentafluoroethane(F125).

[0002] As the compounds F123 and F125 can be used as substitutes forperchlorofluorocarbons (CFC) in the field of aerosols (propellants) andin that of refrigeration, there is currently a search for highperformance processes for their industrial production.

[0003] WO 95/16654 discloses an operation in which F133 a is broughtinto contact at a temperature of 340° C. with chlorine and HF in thepresence of a chromium catalyst. Although the conversion of F133 a inthis reaction is high, it predominantly produces1,1,1,2-tetrafluoroethane (F134 a) at this temperature. Thus, theselectivity of F123 does not exceed 15%, which does not allow productionof this compound under industrially acceptable conditions to beenvisaged.

[0004] WO 94/11327 mentions an operation in which F133 a is brought intocontact, at temperatures of less than 300° C., with chlorine and HF inthe presence of a chromium catalyst. This reaction is carried out with avery large excess of chlorine and of HF and preferably results in theformation of F124 and of F125; thus, the selectivity for F123 remainsbelow 8% and the 110 series/120 series ratio is greater than 10%.

[0005] EP-A-526 908 and EP-A-346 612 provide for the preparation of F123by bringing chlorine into contact with F133 a at a temperaturepreferably lying between 350 and 450° C. in the absence or in thepresence of a catalyst, this chlorination being carried out in theabsence of HF.

[0006] U.S. Pat. No. 4,145,368 provides a process which consists inreacting chlorine with F133 a, and then separating the F123 from thereaction mixture, and in reacting the F113 a resulting from thisseparation with a fresh amount of F133 a, this reaction being carriedout in the vapour phase and preferably between 350 and 425° C. in thepresent of a catalyst, such as a chromium oxide.

[0007] According to this document, the final selectivity for F123 doesnot exceed 29%.

[0008] EP-B-407 990 provides for the chlorination of F133 a to F123 bythermal or catalytic activation in the liquid phase under pressure. Theselectivity for F123 can range from 67.9 to 83.4%, the reaction pressureranging from 50 to 127 bar.

[0009] EP-A-402 874 provides for the reaction of the chlorine with F133a between 350 and 450° C. in the absence of catalyst and of HF.According to this document, the production of F113 a can be eliminatedby virtue of a specific combination of conditions relating totemperature, contact time and molar ratio of the reactants.

[0010] U.S. Pat. No. 5,414,166 provides for chlorination of F133 a inthe presence of hydrogen between 250 and 500° C. and preferably between350 and 450° C.; the selectivity for F123 can range from 65 to 92%.

[0011] U.S. Pat. No. 5,723,700 discloses a stage during which F133 a, HFand Cl₂ react in the presence of a fluorination catalyst between 300 and450° C. to produce essentially F134 a and traces of F123.

[0012] The invention provides a process for the preparation of F123 bychlorination of F133 a, according to which a relatively moderatetemperature is employed.

[0013] The invention also provides a process for the preparation of F123by chlorination of F133 a, according to which the pressure employed isatmospheric pressure or a moderate pressure, for example not exceeding25 bar.

[0014] The invention also provides a process for the preparation of F123by chlorination of F133 a, according to which a chlorination and/orfluorination catalyst is present.

[0015] The invention also provides a process for the preparation of F123by chlorination of F133 a, according to which a selectivity for F123 ofgreater than 50% is obtained.

[0016] The invention also provides such a process, according to whichthe selectivity for F123 is greater than 70%.

[0017] The invention more specifically provides a process for thepreparation of 1,1,1-trifluoro-2,2-dichloroethane (F123) by bringing1,1,1-trifluoro-2-chloroethane (F133 a) into contact with chlorine, thesaid process being characterized in that the said contacting operationis carried out in the presence of HF and of a catalyst under conditionsof temperature and of contact time and with Cl₂/F133 a and HF/F133 amolar ratios such that HF does not substantially react with the F133 aand the F123 formed and promotes the selectivity for F123.

[0018] The invention relates more particularly to a process such that HFdoes not substantially react with the F133 a and the F123 to give morehighly fluorinated derivatives, such as F124 or F134 a.

[0019] In the implementation of the process according to the invention,it is advisable to choose operating conditions such that HF behavesessentially as diluent and/or stabilizer for the reaction and thereactants and not as reactant in a fluorination reaction. Thetemperature conditions, the Cl₂/F133 a and HF/F133 a molar ratios andthe contact time can generally be chosen within the ranges known forthis type of chlorination reaction and such as reported, for example,above with reference to the documents relating to the said chlorinationreaction.

[0020] Purely by way of illustration and which should not, for thisreason, limit the field of the invention, orders of magnituderecommended for the operating conditions in question will be indicatedbelow.

[0021] The temperature of the reaction mixture is generally between 150and 320° C. This temperature is preferably between 250 and 300° C.

[0022] The chlorine/F133 a molar ratio can be between 0.01 and 0.50 andit is preferably between 0.05 and 0.15.

[0023] The HF/133 a molar ratio can generally be between 0.5 and 2.5.For practical reasons, related inter alia to the separation of theproducts for the purpose of the recycling of the unconsumed reactantsand of the HF, a ratio between 0.8 and 1.2 is preferably chosen.

[0024] The time for contact between F133 a, chlorine and HF over thecatalyst can be between 5 and 100 seconds; it is recommended to have acontact time of between 10 and 60 seconds. The contact time iscalculated here as the ratio of the apparent volume of the catalyst tothe total flow rate by volume of the gases fed to the reactor under thereaction pressure and temperature conditions.

[0025] The catalysts which can be used for this invention are thechlorination catalysts which are known to a person skilled in the artand which are resistant to hydracids, such as HF and HCl. However,preference is given to catalysts generally used for fluorinationreactions with HF. Mention may be made, by way of indication, of bulk orsupported catalysts (supported on fluorinated alumina or on charcoal,for example) based on Cr, Zn, Ni or Mg oxide, alone or as a mixture. Forthis invention, preference will be given to mixed catalysts composed ofnickel and chromium oxides, halides and/or oxyhalides deposited on asupport composed of aluminium fluoride or of a mixture of aluminiumfluoride and of alumina, such as disclosed, for example, in Patents FR 2669 022 and EP-B-0 609 124.

[0026] Prior to the chlorination reaction, the catalyst can beconditioned, if necessary by heat treatment in the presence of Cl₂and/or HF, for example by following the method disclosed in EP-B-0 609124.

[0027] When a mixed nickel/chromium catalyst is used, catalystscomprising, by mass, from 0.5 to 20% of chromium and from 0.5 to 20% ofnickel and more particularly those comprising from 2 to 10% by mass ofeach of these metals in a nickel/chromium atomic ratio of between 0.1and 5, preferably in the region of 1, will be recommended.

[0028] As has been specified, the process in accordance with theinvention consists in particular in bringing chlorine into contact withF133 a, in the presence of HF and of a catalyst, under conditions suchthat HF does not substantially react with the F133 a and the F123 formedto give more highly fluorinated derivatives. These conditions areadvantageously chosen within the temperature, molar ratio and contacttime regions indicated above and it would be up to a person skilled inthe art to choose the exact conditions of a reaction taking into accountthe desired result. Thus, from the moment when the temperature parameterwill have been chosen, for example 280° C., it can be advantageous toreduce the Cl₂/F133 a molar ratio, for example around 10%, to obtain thebest selectivity for the 120 series at the expense of the 110 series.Likewise, it will be advisable, for a certain temperature and a certainlevel of chlorine, to choose the contact time making it possible tocombine the appropriate degree of conversion of the F133 a and goodselectivity for F123. Likewise again, the HF/F133 a molar ratio can bechosen, for example, according to the desired or acceptable values forthe 110 series/120 series molar ratio. As has been indicated, thisHF/F133 a ratio can generally range from 0.5 to 2.5, taking into accountthe other reaction conditions (temperature, contact time, Cl₂/F133 amolar ratio), but this HF/F133 a molar ratio is preferably in thevicinity of 1, for example between 0.8 and 1.2.

[0029] The preceding directions demonstrate that the values recommendedfor the operating conditions have an essentially informative role, itbeing known that it would not be departing from the scope of theinvention to use, for one or other of the reaction parameters, valuessituated above or below the values indicated above, provided that suchoperating modifications do not involve a reaction of HF with F133 aresulting in the formation of substantial amounts of more highlyfluorinated derivatives.

[0030] The chlorination reaction can be carried out in the gas phase, ina stationary bed or in a fluid bed, batchwise or, preferably,continuously, with a possibility of recycling HF and unconvertedreactants to the reactor. The hydrochloric acid formed during thereaction is separated, preferably, before the recycling. The F123recovered can be purified by distillation according to the desiredpurity.

[0031] The chlorine can be introduced into the reactor pure or dilutedin an inert gas, such as nitrogen. The materials used for theconstruction of the plant must be compatible with the presence ofchlorine and of hydracids, such as HCl and HF; they can be chosen, forexample, from “Hastelloy” or from “Inconel”, which are resistant tocorrosive media comprising these hydracids.

[0032] The chlorination reaction according to the invention can becarried out at atmospheric pressure or at a pressure greater than thelatter. For practical reasons, the reaction is generally carried out ina region ranging from 0 to 25 bar relative and preferably between 0 and15 bar relative.

[0033] Under operating conditions capable of fouling the catalyst, itmay be prudent to introduce oxygen at a low content with the reactants.This content can vary, according to the operating conditions, between0.02 and 5% with respect to the organic reactants (molar percentage).The oxygen can be introduced continuously or sequentially.

[0034] The process in accordance with the invention makes it possible toprepare F123 from F133 a under moderate temperature and pressureconditions and with an excellent selectivity for F123.

[0035] The starting 1,1,1-trifluoro-2-chloroethane (F133 a) can itselfbe obtained by application of processes which are now well known. F133 acan in particular be prepared by fluorination of trichloroethylene (forexample by following the method 10 recommended by McBee et al., Ind.Eng. Chem., 39, 409-412), by fluorination of F132 b, F130 a or F1122, orby hydrogenolysis of F113 a.

[0036] In the invention, preference is given to F133 a obtained byfluorination of trichloroethylene.

[0037] Another subject-matter of the invention is therefore a processfor the preparation of F123 from trifluoroethylene, the said processcomprising:

[0038] a) a stage of fluorination of trichloroethylene in a reaction, inthe liquid phase or gas phase, in the presence of a catalyst and under apressure resulting, after separation of HCl and heavy products, in amixture of F133 a accompanied by HF entrained in the azeotropic form;

[0039] b) a stage of chlorination of F133 a by bringing the said F133 ainto contact with chlorine in the presence of HF and of a catalyst undertemperature and contact time conditions and with Cl₂/F133 a and HF/F133a ratios such that HF does not substantially react with the F133 a andthe F123 formed.

[0040] In phase a), for a liquid-phase process, use is preferably madeof a catalyst based on antimony salts and the reaction is advantageouslycarried out under a pressure of at least 10 bar absolute.Trichloroethylene can also be reacted with HF in the presence ofchromium oxide or of chromium oxyfluoride in a gas-phase process.

[0041] The F123 can be used as it is, for example as propellant, inrefrigeration and in the manufacture of foams, where it advantageouslyreplaces F11 because of its harmlessness with regard to the ozone in thestratosphere. For this reason, the process in accordance with theinvention, which, by the results to which it leads, can be operated onan industrial level, is particularly advantageous, both starting fromtrichloroethylene and from F133 a.

[0042] The F123 can also be subjected to an additional fluorination andcan thus result in F125 (pentafluoroethane). This reaction can becarried out according to various processes which are now known: thisstage generally comprises bringing F123 (alone or as a mixture withother compounds of the 120 series) into contact with HF in the presenceof a fluorination catalyst, to obtain F125.

[0043] This stage can be carried out in the vapor phase and the catalystcan be chosen from the catalysts whose use is disclosed, for example, inEP-B-609 124 or in the references to which this patent refers, the saidpatent being incorporated here in particular for the conditionsrecommended for this reaction.

[0044] A further subject-matter of the invention is thus a process forthe preparation of pentafluoroethane (F125), the said processcomprising:

[0045] a) a stage of fluorination of trichloroethylene as describedabove and resulting in particular in F133 a;

[0046] b) a stage of chlorination of F133 a as described above andresulting in particular in F123;

[0047] c) a stage of fluorination of F123 by bringing F123 into contactwith HF in the presence of a catalyst, with or without recycling ofF124, it being possible for the fluorination of F124 to form the subjectof a separate stage.

[0048] In this stage, the catalyst is advantageously a mixed catalystcomposed of nickel and chromium oxides, halides and/or oxyhalides, asdisclosed in EP-B-609 124. It is also possible to use catalysts based onchromium oxide or oxyfluoride or based on alumina or on aluminiumfluoride, optionally doped with a metal, such as zinc, nickel or iron.Such catalysts are disclosed, for example, in EP-502 605 or WO 93/16798.Use may also be made of a catalyst of the chromium/charcoal type, suchas disclosed, for example, in EP-A-456 552.

[0049] For this stage, use is preferably made of a mixed catalystdescribed above deposited on a support composed of aluminium fluoride orof a mixture of aluminium fluoride and of alumina.

[0050] The temperature of this fluorination reaction can be between 250and 470° C. and is preferably between 280 and 410° C. The time forcontact between HF and F123 can be between 3 and 100 s, preferablybetween 5 and 30 s. The HF/F123 molar ratio can range from 1/1 to 20/1and preferably from 2/1 to 9/1.

[0051] Although the reaction can be carried out at atmospheric pressure,it is preferable to carry out the reaction under a slight pressure, forexample not exceeding 10 bar absolute and even less than 5 bar absolute.

[0052] The F125 obtained can subsequently be purified, for example byapplication of the methods disclosed in FR-2 758 137 or WO 95/21147, thecontents of which are incorporated here by reference.

[0053] The process for the preparation of F125 from trichloroethylene,which also constitutes a subject-matter of the invention, can be carriedout continuously in a plant such as presented diagrammatically in one orother of the appended figures.

[0054] These figures illustrate a general diagram of the three stages I,II and III of the process in question.

[0055] The plant comprises in particular (see FIG. 1):

[0056] Stage I

[0057] a reactor (100) comprising the catalyst;

[0058] trichloroethylene (101) and HF (102) inlets;

[0059] an HCl distillation column (103);

[0060] a column for separation of F133 a+HF from the heavy products(104);

[0061] Stage II

[0062] a chlorination reactor (200) fed with

[0063] F133 a and HF (202);

[0064] chlorine (201);

[0065] an HCl separation column (203);

[0066] a column (204) for separation of crude F123 (206) from unreactedF133 a (+ in particular azeotropic HF+unreacted Cl₂) , which arerecycled (205);

[0067] Stage III

[0068] a fluorination reactor (300), fed with crude F123 (206/301)originating from the column (204) of the preceding stage, with HF (302)and optionally with crude F124 (310) recycled from the column (309);

[0069] at the outlet of the reactor (300), devices for treating thereaction gases (columns 303, 304 and 305) intended to recover the HClreaction by-product and the unconverted HF and to neutralize thefluorocarbon compounds before their distillation;

[0070] a column (306) which makes it possible subsequently to extractthe F125 (307) at the top, the bottoms (308) subsequently beingdistilled on the column (309) in order to obtain an F124+F123 mixture(310) purified from its content of heavy products, the said mixturesubsequently being recycled to the reactor (300) in order to befluorinated therein to F125 .

[0071] An advantageous alternative form of this diagram is representedin FIG. 2, in which a column (207) makes it possible to purify both thecrude F123 (206) resulting from the column (204) of Stage II and thecrude F124+F123 mixture resulting from the bottom of the column (306) ofStage III: in this alternative form, which makes it possible to feed thereactor (300) with cleaner products, there is no longer any reason forthe column (309) to exist.

[0072] Of course, the industrial plant comprises additional devices withknown uses (bleed, evaporators, superheater, decanters).

[0073] The invention thus also relates to a plant for the production ofF125 from trichloroethylene which comprises at least the sequence ofdevices as represented in the figure.

[0074] The invention will now be illustrated by the following examples,which are only given purely by way of indication.

EXAMPLE 1

[0075] 75 cm³ of Ni—Cr/AlF₃ catalyst (prepared as disclosed in Patent FR2 669 022) are introduced into an Inconel tube with an internal diameterof 21 mm. The catalyst is treated for 15 h with 1 mol/h of anhydrous HFat 350° C. and at atmospheric pressure. Prior to the reaction, the HFflow rate is adjusted to 1.13 mol/h and the temperature to 280° C. ACl₂/N₂ mixture comprising 15 molar % of chlorine is subsequentlyintroduced into the reactor with a flow rate of 0.79 mol/h. Finally,CF₃—CH₂Cl is introduced into the reactor with a flow rate of 102 mol/hand the total reaction pressure is regulated at 15 bar. After reactingfor 6 h, a gas sample is withdrawn for analysis by gas chromatography.Before making the withdrawal, the gas is freed from HF, HCl and chlorineby bubbling into wash bottles comprising water and sodiumhydroxide/sulphite and then dried over CaCl₂.

[0076] The conversion of F133 a is 7% for a selectivity for F123 of 93%.The 110 series/120 series ratio is 3.4%.

EXAMPLES 2 to 7

[0077] Following the same protocol as in Example 1, various conditionswere tested: Conditions Ex. 2 Ex. 3 Ex. 4 Ex. 5 Ex. 6 Ex. 7 Temperature(° C.) 280 280 280 310 280 280 Cl₂/F133a MR 0.13 0.47 0.13 0.14 0.1 0.1HF/F133a MR 2 2.3 2.1 2.1 1 0.7 ct (s) 20 13 38 19 15 32 Results F133aconversion, % 6.2 13.3 10.1 12.2 4.3 10 F123 selectivity, % 93 87 93 8593 74 110 series/ 2.8% 7.8% 4% 5% 1.8% 6.4% 120 series ratio

COMPARATIVE EXAMPLES EXAMPLE 1a Without HF

[0078] 75 cm³ of Ni—Cr/AlF₃ catalyst (prepared as disclosed in Patent FR2 669 022) are introduced into an Inconel tube with an internal diameterof 21 mm. The catalyst is treated for 15 h with 1 mol/h of anhydrous HFat 350° C. and atmospheric pressure. Prior to the reaction, the HF flowis halted and the temperature reduced to 280° C. A Cl₂/N₂ mixturecomprising 15 molar % of chlorine is subsequently introduced into thereactor with a flow rate of 1.13 mol/h. Finally, CF₃—CH₂Cl is introducedinto the reactor with a flow rate of 1.63 mol/h and the total reactionpressure is regulated at 15 bar. After reacting for 6 h, a gas sample iswithdrawn for analysis by gas chromatography. Before making thewithdrawal, the gas is freed from HF, HCl and chlorine by bubbling intowash bottles comprising water and sodium hydroxide/sulphite and thendried over CaCl₂.

[0079] The conversion of F133 a is 10%, for a selectivity for F123 of42%. The 110 series/120 series ratio is 37%.

EXAMPLE 1b Without HF and Without Catalyst

[0080] A Cl₂/N₂ mixture comprising 15 molar % of chlorine is introduced,with a flow rate of 1.3 mol/h, into an empty Inconel tube with aninternal diameter of 21 mm. CF₃—CH₂Cl is subsequently introduced intothe reactor with a flow rate of 2.08 mol/h and the total reactionpressure is regulated at 15 bar.

[0081] After reacting for 6 h, a gas sample is withdrawn for analysis bygas chromatography. Before making the withdrawal, the gas is freed fromHF, HCl and chlorine by bubbling into wash bottles comprising water andsodium hydroxide/sulphite and then dried over CaCl₂.

[0082] The conversion of F133 a is 2% for a selectivity for F123 of 79%.The 110 series/120 series ratio is 15.4%.

1. Process for the preparation of 1,1,1-trifluoro-2,2-dichloroethane(F123) by bringing 1,1,1-trifluoro-2-chloroethane (F133 a) into contactwith chlorine, the said process being characterized in that thecontacting operation is carried out in the presence of HF and of acatalyst under conditions of temperature and of contact time and withCl₂/F133 a and HF/F133 a molar ratios such that HF does notsubstantially react with the F133 a and the F123 formed and promotes theselectivity for F123.
 2. Process according to claim 1,, in which thetemperature is between 150 and 320° C.
 3. Process according to claim 2,in which the temperature is between 250 and 300° C.
 4. Process accordingto any one of claims 1 to 3, in which the Cl₂/F133a molar ratio isbetween 0.01 and 0.50.
 5. Process according to claim 4, in which theCl₂/F133 a molar ratio is between 0.05 and 0.15.
 6. Process according toany one of claims 1 to 5, in which the HF/F133 a molar ratio is between0.5 and 2.5.
 7. Process according to claim 6, in which the HF/F133 amolar ratio is between 0.8 and 1.2.
 8. Process according to any one ofclaims 1 to 7, in which the time for contact between F133 a, Cl₂ and HFover the catalyst is between 5 and 100 seconds.
 9. Process according toclaim 8, in which the contact time is between 10 and 60 seconds. 10.Process according to any one of claims 1 to 9, in which the catalyst ischosen from mixed catalysts composed of nickel and chromium oxides,halides and/or oxyhalides.
 11. Process according to claim 10, in whichthe catalyst is deposited on a support composed of aluminium fluoride orof a mixture of aluminium fluoride and of alumina.
 12. Process accordingto any one of claims 1 to 11, characterized in that it is carried outcontinuously.
 13. Process according to any one of claims 1 to 12, inwhich the starting F133 a is obtained by fluorination oftrichloroethylene.
 14. Process according to claim 13, in which thefluorination of the trichloroethylene is carried out in the liquid phaseunder pressure in the presence of a catalyst based on antimony salts orin the gas phase in the presence of a catalyst based on chromium oxideor on chromium oxyfluoride.
 15. Process for the preparation ofpentafluoroethane (F125) by fluorination of F123 as obtained byapplication of a process according to any one of claims 1 to
 14. 16.Process according to claim 15, in which the F123 is brought into contactwith HF in the presence of a catalyst as described in claim
 10. 17.Process according to claim 15, in which the starting F133 a is obtainedaccording to either of claims 13 and 14, the said process comprising: astage I of fluorination of trichloroethylene to F133 a a stage II ofchlorination of F133 a to F123 a stage III of fluorination of F123 toF125.
 18. Plant making possible the implementation of the processaccording to claim 17, characterized in that it comprises: (FIG. 1) forStage I: a reactor (100) comprising the catalyst; trichloroethylene(101) and HF (102) inlets; an HCl distillation column (103); a columnfor separation of F133 a+HF from the heavy products (104); for Stage II:a chlorination reactor (200) fed with F133 a and HF (202); chlorine(201); an HCl separation column (203); a column (204) for separation ofcrude F123 (206) from unreacted F133 a (+ in particular azeotropicHF+unreacted Cl₂), which are recycled (205); for Stage III: afluorination reactor (300), fed with crude F123 (206/301) originatingfrom the column (204) of the preceding stage, with HF (302) andoptionally with crude F124 (310) recycled from the column (309); at theoutlet of the reactor (300), devices for treating the reaction gases(columns 303, 304 and 305) intended to recover the HCl reactionby-product and the unconverted HF and to neutralize the fluorocarboncompounds before their distillation; a column (306) which makes itpossible subsequently to extract the F125 (307) at the top, the bottoms(308) subsequently being distilled on the column (309) in order toobtain an F124+F123 mixture (310) purified from its content of heavyproducts, the said mixture subsequently being recycled to the reactor(300) in order to be fluorinated therein to F125 .
 19. Plant accordingto claim 18, characterized in that it comprises (FIG. 2) a column (207)which makes it possible to purify both the crude F123 (206) resultingfrom the column (204) of Stage II and the crude F124+F123 mixtureresulting from the bottom of the column (306) of Stage III.